An Overview of Inverse Psoriasis

An unusual form the disease affecting skin folds

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Inverse psoriasis, also known as flexural psoriasis or intertriginous psoriasis, is an unusual type of psoriasis that occurs in skin folds. The facts that it affects the armpits, groin, and under the breasts (rather than extensor surfaces) and lesions are smooth (rather than scaly) are what set cases of inverse psoriasis apart from those of the more common type, plaque psoriasis.

The disease disproportionately affects overweight people and accounts for anywhere from 3% to 7% of all psoriasis cases, according to a 2012 study in Dermatology and Therapy.

The term flexural refers to surfaces of skin that curve, bend, or fold, while intertriginous refers to areas of skin that touch or rub together.

Symptoms

Many aren't aware that there are different types of psoriasis and expect all cases to present with classic signs, such as dry, scaly skin plaques. That is not the case with inverse psoriasis.

Inverse psoriasis lesions are:

  • Scale-free
  • Smooth
  • Deep red
  • Shiny

This is due to the fact that skin folds hold extra moisture and will naturally slough off any loose tissue as the skin surfaces rub together.

For these same reasons, inverse psoriasis lesions can often be painful, particularly in areas where there is excessive skin-to-skin friction. The tissues within skin folds tend to be delicate anyway, increasing their vulnerability to injury.

Because of this, it is not uncommon for fissures (cracks) and bleeding to develop. Warmth and moisture within skin folds also make them a hotbed for bacterial and fungal infections.

The skin folds most commonly affected are those:

  • Around the genitals
  • Between in buttocks
  • Under the breasts
  • In the creases of the groin
  • Within the navel
  • Behind the ears

In people with extreme obesity (defined as a body mass index over 40), lesions can develop within rolls of abdominal skin, under "double chins," between the thighs, and alongside the overhanging skin of the upper arm.

Note, however, that inverse psoriasis can develop exclusively or co-occur with other types of psoriasis, which may come with other signs and symptoms.

Causes

Inverse psoriasis, like all other forms of psoriasis, is an inflammatory autoimmune disease. For reasons poorly understood, the immune system will suddenly regard skin cells as harmful and launch an inflammatory assault to control what it presumes to be an infection. The inflammation causes still-maturing skin cells, called keratinocytes, to develop at an extremely accelerated rate.

As the cells move from the middle layer of skin (dermis) to the upper layer of skin (epidermis), they will start to compress and break through the protective barrier of the epidermis, called the stratum corneum. In doing so, the affected of skin will start to thicken and form the lesions recognized as psoriasis.

Common Triggers

Little is known about why inverse psoriasis presents in the way that it does. Psoriasis, in general, is believed caused by a combination of genetic factors (which appear to predispose you to the disease) and environmental triggers (which "turn on" and actualize the disease).

Among some of the more common triggers of psoriasis are:

  • Stress
  • Smoking
  • Alcohol
  • Certain medications, such as beta-blockers and lithium
  • Infections, especially strep and upper respiratory tract infections
  • Skin trauma, including sunburns, cuts, and abrasion
  • Obesity

With respect to obesity, some scientists have suggested that adipose (fat-storing) cells play a central role in the development of inverse psoriasis. Adipose cells are known to release inflammatory proteins, called cytokines, into surrounding tissues. It is possible that excessive production of cytokines may be enough to trigger a flare at the sites where adiposity is greatest (i.e., skin folds).

Others believe that the Koebner phenomenon plays a part. The phenomenon, in which rash develops along the lines of a skin trauma, affects around 25% of people with psoriasis, according to a 2013 review of studies from Canada.

The very fact that skin folds rub against each other suggests that the Koebner phenomenon may play a role in aggravating, if not inducing, a psoriatic flare.

Diagnosis

There are no lab tests or imaging studies that can definitively diagnosis psoriasis. The diagnosis is primarily based on a visual examination of the skin accompanied by a review of your medical history.

In addition to evaluating the lesions, a dermatologist will look for signs of nail damage (suggestive of nail psoriasis) and evidence of plaque psoriasis on the scalp or other parts of the body. Your medical history may hold clues to support the diagnosis, including a family history of psoriasis or risk factors associated with the disease.

If in doubt, a dermatologist may perform a skin biopsy for evaluation under the microscope. Unlike normal tissue, psoriatic tissue will appear hyperplastic (thickened) with acanthotic (compressed) cells.

Your doctor will also consider all other possible causes to ensure that the appropriate treatment is delivered. The process, known as a differential diagnosis, will assess for diseases with symptoms similar to those of inverse psoriasis and may include:

Treatments

A number of options are available to treat and manage inverse psoriasis. Many of these are the same as those used to treat other forms of the disease. The primary aim of treatment is to alleviate inflammation, either locally or systemically, to bring the skin condition under control.

Depending on the severity of the symptoms, this may include:

With respect to inverse psoriasis specifically, topical antifungals or antibacterials may be used to treat secondary infections that commonly arise in compromised folds of skin. Oral versions may be used in extreme cases. These drugs are not used prophylactically (to prevent disease) due to the risk of drug resistance.

In people with inverse psoriasis, the oral antibiotic Aczone (dapsone) appears especially effective. It is typically prescribed in a 100-milligram (mg), once-daily dose until the infection resolves.

The antifungal terbinafine, commonly used to treat ringworm and athlete's foot, is used with caution as it can sometimes trigger a flare or, worse yet, a severe form of the disease known as pustular psoriasis.

Coping

As a disease closely linked to obesity, inverse psoriasis will almost invariably improve when excessive weight is shed. This is especially true in people with extreme obesity versus those who are simply overweight. By eating right and exercising regularly, ideally under the supervision of a doctor, your overall inflammatory burden can be relieved.

The same applies to smoking and alcohol. No matter how long you have smoked, quitting will render benefits from the moment you put out your last cigarette.

With respect to alcohol, cut back to no more than two to three drink per day maximum. Avoid non-light beer, which is closely linked to psoriatic flares, and opt instead for light beer or wine.

To better cope with the discomfort of inverse psoriasis:

  • Wear loose clothing will breathable fabrics.
  • Avoid tight belts, collars, and sleeves, as well as leggings and skinny jeans.
  • Speak to your doctor about an appropriate fragrance-free antiperspirant. Zinc-oxide-based products are often beneficial.
  • Apply talcum powder, corn starch, and baking soda to skin folds to keep the skin dry.
  • Wash your armpits and groin whenever sweaty with cool water and mild soap. Blot (rather that wipe) skin dry.
  • Place a thin layer of moisturizer on the affected skin before applying topical medications.
  • Keep your living/work spaces cool to avoid perspiration.
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